This invention relates to a cutting mechanism for a paper shredder having two mutually cooperating, one-piece knife rollers whose cutting discs project radially beyond the cylindrical roller core and are axially equidistantly spaced. The cutting discs of the two knife rollers are in an interleaving relationship. The shredder further has strippers which extend into the space between the cutting discs and which are supported on the cutter housing externally of the knife rollers and externally of the passage zone of the material being processed.
A cutting mechanism of the above-outlined type is disclosed, for example, in German Offenlegungsschriften (patent applications published without examination) Nos. 3,112,838 and 3,128,465.
In the known structures, the strippers serve the purpose of preventing the cut strips leaving the cutting mechanism from wedging between the rotary discs of the rotary cutters and thus causing jams in the cutting region. The danger of jamming is particularly significant in those cutting mechanisms whose knife rollers operate in a "cross-cut" method. Such mechanisms thus not only cut the material into comparatively easily removable strips, but additionally sever the material into short snips which wedge particularly readily in the spaces between the rotary discs.
German Pat. No. 2,247,901, to which corresponds U.S. Pat. No. 3,860,180 and German Offenlegungsschrift No. 3,239,060 disclose cross-cutting systems in which the strippers surround the cylindrical roller cores, disposed between the rotary discs, as a closed circular ring at a comparatively small distance from the roller core. The strippers are stamped of sheet metal by punching, in one process step, a closed, circular hole in the stripper. Such a stripper construction, however, requires that the knife roller not be made of a one-piece solid material. Rather, to be able to use such a stripper design, the cutting discs must be made of parts that are separate from the roller core and must be inserted fixedly on the core with the interposition of the strippers. The strippers too, are inserted or threaded onto the roller core by virtue of their circular recesses. The required multipart configuration of the rotary cutters poses problems after a long (multi-year) use, because the close dimensional tolerances required for a highly satisfactory cutting operation cannot be maintained with sufficient reliability.
The present invention therefore improves on the known, one-piece rotary cutters made of solid material. In the known cutting mechanism employing one-piece rotary cutters, two strippers are associated with each space between two rotary discs of one and the same knife roller. The strippers are arm-shaped, oriented at approximately 90.degree. to the direction of passage of the material being processed and fill the space between two rotary discs on the intake and outlet side, with their ends resting against the roller core, thus holding the cut strips in the region of the conveying gap and preventing them from entering into the spaces between adjoining rotary discs. Such strippers, however, are not suitable to meet the greater demands of a cutting mechanism of the cross-cut type, because they shield the roller core outwardly only over about one-half of its circumference.